This invention relates to a hydrometallurgical process for the recovery and separation of valuable products from a sulfate or chloride pregnant leach solution, or both.
Polymetallic orebodies containing multiple valuable metals at lower grades are becoming increasingly attractive for resource companies to assess their potential for exploitation, despite the greater metallurgical challenge in the recovery and separation of such elements into saleable concentrates or products. This is generally the case for ores containing precious metals (PMs) such as platinum group metals (PGMs), gold or silver and other valuable metals such as nickel, cobalt, copper, rare earth elements (REE) including yttrium and scandium, as well as uranium, thorium, manganese, zinc, cadmium, molybdenum, vanadium, titanium and other minor elements such as vanadium, germanium and gallium.
Current hydrometallurgical process routes for extraction of valuable metals from polymetallic orebodies are described in International Patent Publication No. WO 99/60178, known as the “Kell Process” (see FIG. 1), International Patent Application No. WO2014/009928, and Australian Patent Application No. 2013263848 (the contents of each of which are incorporated herein by reference). All of these processes require as the starting material an ore or a concentrate of the ore and produce one or more leach liquors containing dissolved valuable metals and other elements.
The core of the Kell Process route (or “core Kell process”) comprises the steps of:                (i) leaching an ore or concentrate made from an ore in a pressure oxidation sulfate leach to dissolve base metal sulfides contained in the ore or concentrate and forming a sulfate leach filtrate containing base metals and a residue containing precious metals (PMs);        (ii) separating the sulfate leach filtrate from the residue;        (iii) roasting or heat treating the residue to form a calcine; and        (iv) leaching the calcine in a chloride leach to dissolve the PMs into solution forming a chloride leach filtrate for PM recovery and a solid waste residue.        
Selection of the process route for recovery and separation of valuable elements from both sulfate and chloride pregnant leach solution (PLS) for any specific application is driven largely by project-specific criteria such as end-product requirements, as well as ore and concentrate assay suite and mineralogy. Production of market-driven end-products, such as separate PMs, oxides, salts or other products, as well as mixed high-grade concentrates with particular impurity profiles may be required, for example.
The PGMs, gold, silver and other value elements are in some cases recovered from the chloride PLS by adsorbing these elements onto ion-exchange (IX) resins or other sorbent media and subsequently recovering the elements by elution, for example using a thiourea solution. PMs can be precipitated from the eluate using a caustic, ammoniacal or reductant solution to form one or more high-grade PM concentrate products for direct sale or refining, as described in International Patent Publication No. WO 99/60178. Alternatively, the loaded resin or sorbent can be incinerated directly to produce a high-grade PM concentrate product for refining, or may be shipped directly to the refinery.
However, in other cases, production of end products with certain targeted specifications may be required, whereby such specifications are best achieved via alternative methods.
Thus, the direct IX route described above is not always optimal for all feed and product types, such as for cases where the PLS contains elements or species at levels that may interfere with the IX adsorption process. An alternative process for the recovery and separation of PMs and other valuable elements from PLS that meets the criteria for other feed and product types is therefore needed.
Moreover, additional valuable elements are contained in the leach process streams described in steps (i) and (iv) above, and these valuable elements may equally warrant recovery and/or recycling and/or separation into added-value products.
An alternative process for the recovery and/or recycling and/or separation of PMs and other valuable elements from PLS to produce saleable high-grade value metals and/or metal cathodes, powders, salts or precipitate products thereof would therefore be very useful.